1. Field of the Invention
This invention relates to a two-stage process for the production of alpha-beta carboxylic acids through catalytic vapor-phase oxidation of olefins by molecular oxygen using mixed metal oxide catalysts having the formulas A) MoaPdbBicFedX1eX2fX3gOz (X1=Co, Ni, V, Pt and/or Rh; X2=Al, Ga, Ge, Mn, Nb, Zn, Ag, P and/or Si; X3=K, Mg, Rb, Ca, Sr, Ba and/or Na); and B) Moa1Vb1Alc1Xd1Ye1Oz1 (X=W or Mn or both; Y=Pd, Sb, Ca, P, Ga, Ge, Si, Mg, Nb and/or K). The exothermic nature (exothermicity) or xcex94T of the oxidation reaction can be controlled by addition of oxygen at an intermediate stage of the process while achieving same high output yield and catalyst life of the overall reaction.
2. Description of the Related Art
A two stage vapor phase oxidation process for the production of acrylic acid from propylene is well known in the art. Attempts have been made to improve the productivity of a process for production of acrylic acid by using different types of catalysts and process parameters, described, e.g., in JP1165543; JP59013746; EP911313; U.S. Pat. No. 5,602,280 (EP0630879); EP145469; U.S. Pat. No. 5,218,146 (EP293224); U.S. Pat. No. 4,365,087 (DE3002829); and U.S. Pat. No. 5,077,434. For example, U.S. Pat. No. 5,218,146 describes a process for the production of acrylic acid by a two-stage catalytic vapor-phase oxidation of propylene with molecular oxygen: the first stage oxidizes propylene to produce mainly acrolein and the second stage oxidizes acrolein to produce mainly acrylic acid. In this process there is supplied to the first stage reaction, a raw gas containing a saturated aliphatic hydrocarbon having 1 to 5 carbon atoms in an amount in the range of 5-70% by volume, carbon dioxide in an amount in the range 3-50% by volume, aliphatic hydrocarbon and carbon dioxides in a total amount in the range of 20 to 80% by volume and the gas also contains steam in an amount in the range of 0.5 to 8 mol per mol of propylene.
Further process improvements are needed to deal with problems in the removal of heat of the reaction, in space velocity, in limitations on the life of the catalyst due to ineffective heat removal and in limitations in catalyst activity related to its composition.
It is an object of the present invention to provide a substantially safe process for the production of acrylic acid by the catalytic vapor phase oxidation of propylene with a high productivity.
It is a further object of the invention to provide a process for the production of an acrylic acid or methacrylic acid from propylene or isobutylene in which xcex94T of reaction is lower because of the specific composition of catalysts. A lower xcex94T enhances the life of the catalyst.
It is another object of the invention to provide a process which exhibits long-term operation or stability in term of catalyst performance by intermediate addition of oxygen in between the two stages of the process, or at multistages in the process.
The invention relates to a process for the production of carboxylic acids using a two-stage catalytic vapor-phase oxidation of olefins. The invention also includes a new catalyst for the first stage of the process.
The process comprises:
introducing into a first stage reactor, a feedstream comprising olefins, oxygen, steam and inert gas,
subjecting the feedstream to oxidizing conditions in the first stage to produce an intermediate product stream comprising aldehydes;
introducing the intermediate product stream into a second stage reactor under aldehyde oxidizing conditions to produce a second stage product comprising carboxylic acid.
Besides introduction of oxygen into the first stage, oxygen can also be introduced into the product stream intermediate between the first and second stages or at multistages within the same reaction zone or reactor.
Moreover, the second stage product is a mixed reaction gas which contains off-gas and carboxylic acid product. Off-gas obtained by separating carboxylic acid from the second stage mixed reaction gas product can be recycled to the first stage. In addition, steam can also be present in the second stage mixed reaction gas product. Steam obtained by separating the carboxylic acid product from the mixed reaction gas product can be supplied to the first stage.
The olefins are, for example, ethylene, propylene, or iso- or n-butylenes; and the aldehydes are, for example, acetaldehyde, acrolein and methacrolein, producing corresponding carboxylic acids.
In a first stage, olefins are oxidized to produce an intermediate product stream containing alpha-beta unsaturated aldehydes using catalyst A having a composition according to the formula
MoaPdbBicFedX1eX2fX3gOz,
wherein
X1=one or more of Co, Ni, V, Pt, Rh;
X2=one or more of Al, Ga, Ge, Mn, Nb, Zn, Ag, P, Si, W;
X3=at least one or more of K, Mg, Rb, Ca, Sr, Ba, Na; and
O=oxygen (which satisfies the valences of the other elements);
and wherein
a, b, c, d, e, f, g, and z are as defined below.
In a second stage, alpha-beta unsaturated aldehydes in the intermediate product stream are oxidized to produce mainly alpha-beta unsaturated carboxylic acid using catalyst B having a composition according to the formula
Moa1Vb1Alc1Xd1Ye1Oz1
wherein
X=W or Mn or both;
Y=at least one or more of Pd, Sb, Ca, P, Ga, Ge, Si, Mg, Nb, K; and
O is oxygen which satisfies the valences of the other elements;
and wherein
a1,b1,c1,d1,e1 and z1 are as defined below.
In a preferred embodiment, the invention relates to a process for the production of alpha-beta carboxylic acids, such as acrylic acid or methacrylic acid, by the catalytic vapor-phase oxidation of olefins, such as propylene or isobutylene. More particularly, the invention relates to a process for highly efficient production of acrylic acid or methacrylic acid through the use of a feed gas having a particular composition. In the production of acrylic acid by a two-stage catalytic vapor-phase oxidation of propylene with molecular oxygen, a first stage oxidizes propylene to produce mainly acrolein and the second stage oxidizes acrolein to produce mainly acrylic acid.
In preferred embodiments, a gas mixture is supplied to the first stage. The gas mixture preferably contains unsaturated aliphatic hydrocarbon of about C1 to C5, most preferably propylene or isobutylene, in an amount from about 3% to about 90%; oxygen in an amount from about 2% to about 50%; steam in an amount from about 5% to about 50% by volume; and 5% to 80% inert gas or gas with high specific heat such as nitrogen, argon, propane, carbon dioxide.
Additional oxygen in an amount from about 2% to 50% can be added at an intermediate stage of the process or at multiple stages in the reaction zone, in order to control the total oxidation reaction and to achieve a long catalyst life and high productivity of the acrylic acid. The part of the amount of oxygen added at an intermediate stage or multistage is preferably from about 2% to about 15% by volume.
A catalytic process according to the present invention shows improvement in the catalyst performance and/or good catalyst stability. While it is not intended to be bound by theory, it is believed that these improvements can be attributed to low xcex94T of the reaction and introduction of oxygen at multi- or intermediate stages of the reaction zones to control the extent of exotherm and keep. the reaction mixture out of explosive regimes or explosive ranges. Moreover, catalysts provided to carry out the reactions are relatively active at lower temperature than temperatures described in the prior art.